I had a long conversation with my sailplane Guru friend last evening and he
insisted that the bumps left by the barnacles do indeed cause a fair amount
of drag...I'm still not totally convinced but I guess I'll bite the bullet
and sand all of those little suckers off today. Yuck! I do use the best
ablative I can buy and the last bottom job lasted over 2 years with very
little growth but during the last year(the 3rd year) there was a lot of
growth down about 8" from the waterline but very little below the chine.
QL
"K. Smith" wrote in message
...
Sail-n-Dive wrote:
K,
you sound like you have some experience with bottom jobs and I'm not
being smart here, but HOW does it matter? Drag? Poor adhesion of the
paint? I doubt if there is laminar flow over the bottom of a boat with
ablative paint and surely the few thousands of an inch left would not
have much if any effect. I'm going to get as much as I can without
spending too much time.

With a displacement hull surface fairness & finish "is" important, indeed
see the extraordinary lengths racing yachts or racing powerboats go to the
ensure both.

By giving it a quick sand with an orbital sander you repeatedly over time,
knock the tops off the high spots & equally allow the low spots to become
filled (with paint). Of course the opposite is true if you allow things
like barnacle bases to remain, they get buried under layers of paint & so
the uneven surface just gets worse with every season.

One real problem that I have is getting the centerboard slot in the short
cast iron keel well prepped. I'm going to try sand blasting it this time
but it is very narrow and I'm not sure that I can do that. I used hammer
and long chisel last time but I was fighting growth 6 months after I put
it in the water. I'd really like to put a lift on my pier but it's tough
to do.

I hate to be the bearer of bad news but 6 mths is about right for the mid
price antifouls, the much more expensive ones (ablative) will go 12 mths,
however only if applied in the thicknesses as given usually on the tin,
you'll be surprised how much is needed (at "least" two full on coats).
You'll find the sellers of the paint always tell you "your" area is
particularly bad for fouling but .................

K

QL
"K. Smith" wrote in message
...

Wayne.B wrote:

On Sat, 22 Jan 2005 11:23:47 -0600, "Sail-n-Dive"
wrote:


I really left the Paceship in too long this time and have a fair amount
of barnacles. I've done many bottom jobs and have never tried to get
every last bit of the barnacle off as long as it was relatively smooth.
For a hull speed boat, I can't see the harm. I'm using a very high
quality ablative bottom paint this time and want to be sure that it's a
lasting job. Any INFORMED comments?

===========================

I had ablative bottom paint on my small boat and had good luck
removing marine growth of all kinds using a standard Mark I, Home
Despot pressure washer (~~$450 variety). Of course it also removes
most of the bottom paint, at least the ablative active ingredients,
but if you're getting ready to repaint that's not a problem. I've now
gone to a hard paint with a biocide in it that seems very effective,
believe it's called Micron Extra with biolux slime blocker.



It "does" matter & probably even more so with a displacement hull, so
getting all the old barnacle off is worth the effort, although granted
it's depressing job:-)

Get all the old loose paint off with a water blaster as above, then
scrape all the barnacles off.

As you are obviously aware, it's difficult to get the base of well
established barnacles off with a scraper & not cut into the underlying
paint so it's best to give the whole bottom a "quick" sand with an
orbital sander.

So long as you water blasted all the old loose or soft antifoul off, it
shouldn't clog & you'll quickly see which grit of paper suits the surface
(use as fine as will not clog but still knock the high spots off the
existing paint). You're not trying to remove or even sand through the
remaining paint, just flatten the surface & rough it up a little for the
repaint.

When you come to a barnacle base left after the scraping, just slow down
on that till you sand it away, they're hard & orbital sand off pretty
easily.

If you're changing to a new style of anti foul say going to soft ablative
from the harder types then; when it's sanded smooth & surface slightly
roughed give it a couple of barrier coats & another very quick light sand
before the anti foul.

Wear a mask when sanding antifoul even if there doesn't appear to be much
dust.

K